Why can’t iPhone support WhatsApp backups on Google Drive instead of iCloud?

I find it frustrating that iPhones don’t allow WhatsApp chats to be backed up to a preferred cloud service, like Google Drive, rather than only iCloud. I already have ample storage on Google Drive, but it feels like I’m being forced to buy more iCloud storage just for WhatsApp backups. It would be great if Apple provided an option for users to select their cloud service for app backups.

Anyone else feel the same way?